The present invention relates to the removal of impurities from iron and, more particularly, to the removal of tin from molten iron by chlorination.
It is well known that removal of tin by direct oxidation from iron/tin solution is impossible since, at steelmaking temperatures, iron oxide is more stable than tin oxide. The standard free energy of formation of iron oxide at 1800.degree. K is about -35K cal/gm mole whereas the standard free energy of formation of tin oxide is -27K cal/gm mole. In other words, iron oxide forms prior to tin oxide in an oxidation process so that removal of tin by oxidation has not been achieved practically.
The primary object of the present invention is to provide a process for converting tin, which is dissolved in molten iron, into tin oxide by converting the tin to gaseous tin chloride, reacting either the gaseous tin chloride or tin chloride in condensed form with oxygen to form tin oxide and free chlorine, separating the tin oxide from the gas by filtering and recycling the gaseous chlorine into the iron bath. Some other metals dissolved in iron and some iron generally will be evaporated during the chlorination process together with the tin. Since the cost of oxygen is substantially lower than the cost of chlorine, the total operating cost of the present process is substantially lower than that of direct chlorination. Approximately 70% to 95% of the chlorine gas used in chlorination of molten iron bath becomes available for recycling in the present process.
Other objects of the present invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the process, and its steps, which are described in the present disclosure and defined in the appended claims.